Abstract

PURPOSE: Currently, the most widely used method of treatment of urinary tract stones is extracorporeal shock wave lithotripsy (SWL).Patient and stone characteristics are important for SWL success. We evaluated noncontrast computed tomography (NCCT) characteristics of urinary tract stones for the prediction of SWL success. METHODS: Records of patients who underwent NCCT before SWL treatment between January 2008 and June 2012 were retrospectively evaluated. Demographic data were recruited from patient files. Hounsfield units (HU), stone size and skin-to-stone distance (SSD) were measured on NCCT. After serial measurements of the highest HU value (HUmax) and lowest HU value (HUmin), HU value was calculated as the average of these two values (HUave). These parameters were compared between successful [stone-free (SF) group] and unsuccessful [residual fragment (RF) group] cases after SWL. RESULTS: A total of 254 patients, 113 kidney stones and 141 ureteral stones, were evaluated. Mean age was 51.0 ± 14.6 (18-87) years, and mean stone size was 10.9 ± 3.7 mm. Stone diameter, HUmax, HUmin and HUave were significantly lower in SF group when compared with RF group for both kidney and ureteral stones (p < 0.05). We also found that SSD for kidney stones was predictive for SWL success.CONCLUSIONS: We suggest that HUmax, HUmin and HUave values are significant predictors of SWL success for both kidney andureteral stones. They might be used in daily clinical practice for patient counselling.

Int Urol Nephrol. 2015 Jan;47(1):69-73. Epub 2014 Oct 14.

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Comments
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Several attempts have been made to predict the outcome of SWL. Similar to another study recently published [1], some stone characteristics were analysed in this article. Accordingly stone-free rates were related to stone size, skin-to-stone distance, minimum, maximum and average HU as well as HU density (the latter estimate obviously obtained by dividing the HU by the stone diameter, not stone surface area or volume).

It is surprising that the overall stone-free rate for stones in the kidney was not better than 29% and that for ureteral stones only 51%. Those results were recorded despite average numbers of SWL sessions of 2.78 and 2.57, respectively.

The authors used 750 Hounsfield units as discriminator for good and poor stone clearance. It is not mentioned to which extent clearance was related to insufficient disintegration or to other factors. The HU-limit used is lower than that usually mentioned in the literature.

The results might be useful for patients treated with this specific lithotripter, but as shown in other reports other limits of relevant variables probably should be applied with other lithotripter systems.

Several attempts have been made to predict the outcome of SWL. Similar to another study recently published [1], some stone characteristics were analysed in this article. Accordingly stone-free rates were related to stone size, skin-to-stone distance, minimum, maximum and average HU as well as HU density (the latter estimate obviously obtained by dividing the HU by the stone diameter, not stone surface area or volume).
It is surprising that the overall stone-free rate for stones in the kidney was not better than 29% and that for ureteral stones only 51%. Those results were recorded despite average numbers of SWL sessions of 2.78 and 2.57, respectively.
The authors used 750 Hounsfield units as discriminator for good and poor stone clearance. It is not mentioned to which extent clearance was related to insufficient disintegration or to other factors. The HU-limit used is lower than that usually mentioned in the literature.
The results might be useful for patients treated with this specific lithotripter, but as shown in other reports other limits of relevant variables probably should be applied with other lithotripter systems.
Reference
1. Torricelli FC, Marchini GS, Yamauchi FI, Danilovic A, Vicentini FC, Srougi M, Monga M, Mazzucchi E.Impact of renal anatomy on shock wave lithotripsy outcomes for lower pole kidney stones: results from a prospective multifactorial analysis controlled by computed tomography scan.
J Urol. 2014 [Epub ahead of print]